The use of composite materials in the design of aircraft and spacecraft today is becoming increasingly prevalent due to the light-weight and relatively high-strength properties achievable with those materials, among which fiber-reinforced polymer composites, such as carbon fiber reinforced polymers (CFRP), are especially preferred. For composite panel members having a foam core sandwich structure, physical properties of composite materials are not always advantageous, however. For example, the infusion or impregnation with a high-temperature resin that is typical with conventional molding techniques, like modified vacuum infusion (MVI), vacuum-assisted resin transfer molding (VARTM), or vacuum-assisted process (VAP), can lead to high residual stresses in the foam core due to a mismatch between the coefficients of thermal expansion (CTE) for the different components of the sandwich structure.
Very recently, the present applicant and assignee developed a method of producing or manufacturing a composite panel member having a sandwich structure that essentially overcomes the above problem of high residual stresses in the core. That new method or technique will be referred to as the “ZZ-process” or “ZuKZaG-process” and is described in detail in published International Patent Application WO 2012/025241 A2, the entire contents of which are incorporated herein by direct reference. In comparison with the MVI-process, the ZuKZaG-process results in somewhat longer production times or lead times. In FIG. 4 of the drawings, this comparison of the ZZ-process with the conventional MVI-process is illustrated by a chart or graph that schematically shows the variation of the temperature (vertical axis) over the duration of the process (horizontal axis). The end of the ZuKZaG-process (at or close to room temperature) is reached at a time (Δt) after the end of the MVI-process.